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Repackaging (for example MP4 to MKV) is instant on a phone. A full re-encode, such as to WebM, is slow — on a phone, keep those clips under about 1 minute.
Repackaging (for example MP4 to MKV) is instant on a phone. A full re-encode, such as to WebM, is slow — on a phone, keep those clips under about 1 minute.
Convert between MP4, WebM, and MKV right in your browser — free, private, and no software to install.
Drag & drop your video here, or click to browse
MP4, WebM, MOV, or MKV — up to 500MB
Upload a video to convert its format
This free tool converts video between MP4, WebM, and MKV entirely inside your browser using ffmpeg. When your video's codec is already compatible with the target format, it's remuxed instantly instead of being re-encoded — otherwise it's re-encoded at the quality level you choose.
Is my video uploaded to a server?
No. The conversion runs locally in your browser using ffmpeg.wasm — your video is never uploaded anywhere.
What formats can I convert between?
You can convert between MP4 (H.264/AAC), WebM (VP9/Vorbis), and MKV. MKV can also be used as a source format.
Will converting reduce my video's quality?
Only if a full re-encode is needed. When your video's codec already fits the target container, it's copied byte-for-byte with no quality loss at all.
Which format should I choose?
MP4 is the safest choice for playback on nearly any device or platform. WebM produces smaller files for web use and supports efficient VP9 video. MKV is the most flexible container and a good pick when you just need to hold your existing streams without re-encoding.
Why did my file get larger after converting?
Different codecs compress differently. Converting from a highly compressed format like H.264 to a less efficient setting, or re-encoding at a higher quality level, can produce a larger file even though nothing else changed.
Why was my conversion instant this time?
When your video's existing codec is already valid inside the target container (for example, H.264/AAC video going into MKV), we remux the streams directly instead of decoding and re-encoding them — that's what makes it finish almost instantly with zero quality loss.
Your video is processed entirely on your device. It is never uploaded to our servers, keeping your content completely private.